Fuse element and a high voltage current-limiting fuse

ABSTRACT

A fuse element essentially consisting of a plurality of fuse wires twisted together and press rolled under the twisted state and a high voltage current-limiting fuse which comprises at least one of the above mentioned fuse elements wound spirally with a given pitch around an insulating core embedded in an arc quenching filler within an insulating tube closed at the ends thereof by external and internal electrodes connected to the ends of the fuse element. The presence of the fuse wires twisted together and rolled under the twisted state makes it possible to refrain the overvoltage from sudden rising in a positive manner. The fuse element with a low melting point alloy portion incorporated therein and assembled within a Teflon sleeve is capable of reliably interrupting the full-range of fault currents.

United States Patent 1191 1 6m et al. p i July 23, 1974 54] FUSE ELEMENT AND AHIGH VOLTAGE 3,148,257 9 /1964 Feenan et al 337/295 CURRENT LIMIT[NG US 3,287,524 11/1966 Huber et al..... 337/290 1 3,471,3l8 10/1969 Koch; 337/295 [75] Inventors: Yoshio Ono; Chiu Sekine, both of -Nobuyoshi' Asai, both of lnuyama, 207,786 11/1939 Switz e 1 "l ar 1 d 33 7/22 4 1 all of Japan 237,934 3/1960 Australia 337/161 [73] I s f rg fggfgg g works Primary Examiner-J. D. Miller Assistant Examiner-Fred E. Bell [22] Filed: Nov. 5, 1971 Attorney, Agent, or Firm--Silverman & Cass 211 Appl. No.: 196,039

, g [5 7 ABSTRACT F i A li ti Pri it D A fuse element essentially consisting of a plurality of 1 Nov H 1970 Japan 99578 fuse wires twisted together and press rolled under the f 1970 Japa 49w] twisted state and a high voltage current-limiting fuse Sept' 2 1971 Japan '1 4667620 which comprises at least one of the above mentioned T IIIIII u fuse elements wound spirally with a given pitch 2 n 1 around an insulating core embedded in an arc quench- 1 U C 0 ing filler within an insulating tube closed at the ends [51] Int i 6 /04 thereof byexternal and internal electrodes connected dd .161- 2 tothe ends of the fuse element. The presence of the 337/293, 29/6151 02 1711/1 fuse wires twisted together and rolled under the I A 117 F 119 R twisted state makes 1t,poss1ble to refram the overvolti p age from sudden rising in a positive manner. The fuse 1 element with a low. melting point alloy portion incor- [5'6] I porated therein and assembled within a Teflon sleeve 1 is capable of reliably'interrupting the full-range of 587,764- 8/1897 Short.... 174/129 R f lt currents 1,579,596 4/1926 Cote 337/290 1,629,266 5/1972 Feldkamp 337/296 15 Claims, 24 Drawing Figures PAIENIEBmzamu V SHEEIMJF 5' m Qm Qt m wt Qm wt mw .1 FUSE ELEMENT AND A HIGH VOLTAGE CURRENT-LIMITING FUSE BACKGROUND-OF THE INVENTION I; Field of thelnvention I I i "This invention relates to a fuse element and a high voltage current-limiting fuse which employssaid fuse element comprising at least one fuse element wound spirally with a given pitch around an insulating core embedded in an arc quenching filler within an insulating tube closedat the ends thereof by external'and internal electrodes connected to the endsof the fuse element. I

2. Description of the Prior Art I In theabove mentioned kind of current-limiting fuse thereis produced an overvoltage when a high current' is interrupted by the current-limiting fuse.

The sudden rise of the overvoltage thus produced must. be kept as small as possible bytaking the mutual relation between the overvoltage on the one hand and the firing. potential across an arrestor, the flashover voltageacross a transformer, electric motor, etc., and

the;fl ashover voltage across an electric insulator mounted on transmission lines on the other hand into consideration for the purpose of bringing the overvoltage into insulator coordination with the arrestor, transformer, electric motor, electric insulator, etc.

Heretofore, it 'has been the common practice as I means'forsuppre'ssing the overvoltage to use a current limiting fuse whose fuse element has portions which are irregular in cross section. These irregular portions having different cross sections areformed by deforming thefuse element into meshes, perforating regular holes in a-metal ribbon of fuse element material, forming meshes in a metal .sheet of fuse element material with the aid of a punching press or forming regular reduced portions ion a linear fuse element by means of aham- I me'ring treatment. I I

- Thecurrent-limiting tioned fuse element serves to suppress the sudden rise of overvoltage to a certain degree.

However, the use of the aforesaid prior art fuse elements has a number of disadvantages. In the first place,

- itis not sufficient enough to suppress thesudden rise of overvoltage in rapid and reliable manner, 'while-it is technically difficult and requires a number of steps to manufacture the fuse elements. Secondly, the fuse element comprising a metal sheet of fuse element-material punched into meshes or the linear fuse element with reduced portions must be manufactured by means of a. press mould which has accurately been finished; Third,

thefuse element with reduced portions is liable to be broken when itis wound around an insulating core at the reduced portions with the result that it is difficult to obtain a fuse element having an excellent quality and being stable in operation. Fourth, the conventional fuse element must be embedded in large amount of arc quenching filler in ,order to refrain the overvoltage from sudden rising and to interrupt a low current in a end of air-insulating core when the conventional fuse fuse having the above men- SUMMARY OF THE INVENTION It is therefore a main object of the present invention to provide a fuse element which can be manufactured in an extremely simple and easy manner and-can be A still further object of the invention is to provide a current-limiting fuse which is small in size and is capable of indicating the rupture of the fuse element in a positive manner. I

A still further object of the invention is to provide a current-limiting fuse comprising at least one fuse element whose ends can be secured to'internal and external electrodes in an extremely simpleand easy manner.

A still another object of the inventionis to provide a current-limiting fuse whose fuse element is provided at s its one portion with a low meltingpoint alloy portion and with. a Teflon sleeve spaced around the low melting point alloy portion and which is capable of preventing the Teflon sleeve from being deteriorated by heat generated by a current flowing through the fuse element.

' BRIEF'DESCRIPTION OFTHEDRAWINGS The present invention will be more fully understood by reference to the following preferred embodiments, byway of example, andclaims taken in connection with the appended drawings, in which:

.away to show afuse element in non-ruptured state} FIG. 4 shows the same fuse element as FIG. 3

in the ruptured state;

FIG. 5a is an enlarged front elevation shwoing'one I embodiment of the fuse elementaccording to the invention, parts being broken away; 7

FIGS. 5b, 5c and 5d are sections on lines I-I, II--Il and III-III of FIG. 5a, respectively;

FIG. Se is an enlarged simplified view for assisting in the description of that portion of the fuse element which-is near the line III-III of FIG. 5a:

FIG. 6a is anenlarged front elevation showing another embodiment of the fuse element according to the invention, parts being broken away;

FIGS. 6b, 6c and 6d are sections on lines IVIV, VV and-VL-VI of FIG. 6a, respectively;

FIG. 7a is an enlarged front elevation showing a further embodiment of the fuse element according to the invention, parts being broken away;

FIGS. 7b, 7c, 7d, 7e and 7f are section on lines VII- -VII, VIII-Vlll, IXIX, XX and XIXI of FIG. 7a, respectively;

FIGS. 8a, 8b and 8c are graphs to show the experimental results invention, conventional fuse elements compared with the fuse element according to the invention; 1

FIG. 9 is an exploded perspective view of the essential parts of the current-limiting fuse according to the in vention, in which a part of the fuse element is covered with a Teflon sleeve; and

- FIG. 10 is a schematic partial view of a fuse element and Teflon sleeve assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, especially FIGS. 1, 2 and 3 showing a preferred embodiment of a current-limiting fuse according to the invention, numeral 1 designates an elongated hollow insulating core provided at its outer surface with a plurality of ridges 2 extending in parallel with the longitudinal axis. Each end-portion 2a of the ridges 2 is reduced in height and to 'eachend portion 2a is secured a cap-shaped internal electrode 3. The internal electrode 3 is provided at its lower skirt portion 4 with a plurality of tongues 5 separated each-other by slits 6. The internal electrode 3 is providedat its upper fiat portion with a small cylinder portion 7, arranged coaxially with the lower skirt portion 4 and provided with a plurality of tongues 8 separated from each other by'slits 9.

To the internal electrode 3 is secured a cap-shaped external; electrode 10. provided at its end face 11 with an annular indentation l2 and-provided at its center with a center opening 13- adapted to be extended through by the small cylinder portion 7 of the internal electrode 3.

Numeral 14 designates an insulating tube of insulating material such as resin, porcelain, glass, fiber, paper, etc. The insulating tube 14 concentrically surrounds the insulating core 1 located at the center axis and each end of the insulating tube 14 is inserted into the external electrode 10 and secured thereto.

A chamber formed by the outer surface of the insulating core 1 and the inner peripheral surface of the insulating tube 14 is filled with an arc-quenching filler 15 such as silica sand, magnesia, etc., which is available in this art. C

At least one fuse element 16 of silver or other suitable material such as copper is spirally wound around the insulating core 1 preferably with a given pitch. In FIG. -1 there is shown two fuse elements 16 spirally wound and spaced around the insulating core 1 for ease of illustration. In practice, however, the two fuse elements 16 are spirally and closely wound around the insulating core 1 and brought into contactwith the ridges 2 thereof. Each end of the fuse element 16 after being fixed by the tongue 5 formed at the lower skirt portion 4 of the internal electrode 3 is also fixed by the tongue 8 formed at the small cylinder portion 7 of the internal electrode 3 and secured thereto.

Although the two fuse elements are shown in FIGS.

1 and 2, the number of the fuse elements is not limited to two and use may be made of at least one fuse element.

The tongue 5 encircled by the fuse element 16 may be bent slightly inwards so as to prevent the fuse element 16 from being disengaged from the tongue 5 as shown in FIGS. 1 and 2.

The hollow insulating core 1 is provided at its center with a bore la which serves to lead through a resistor wire 17. The resistor wire 17 may preferably be formed of stainless wire, titanium wire or other suitable resistor wires used in this art having a high resistivity and tensile strength. The resistor wire 17 is connected at its one end through the internal electrode 3 to the external electrode 10 in the same manner as the fuse element 16 which is connected to the internal and external electrodes. The free end of the resistor wire 17 is connected to an indicator piece 18 which may suitably be constructed by a semi-sphere shapedpiece and preferably coloured for ease of clear discrimination.

The resistor wire 17 is provided at its intermediate region with a coiled portion 19 whose one end is connected through a connector piece 20 and a rectilinear tensionresisting portion 21 to the indicator piece 18.

The tension resisting portion 21 is surrounded at that portion which extends through the internal electrode 3 and external electrode 10 by a heat insulating tube 22 of suitable heat insulating material such as porcelain, glass, etc., which used in this art. The heat insulating tube 22 serves to thermally insulate the internal electrode 3 and external electrode 10 from the tension resisting portion 21 which is adapted to be melted when the fuse element 16 is ruptured.

The tongues 8 of the internal electrode 3 are folded and located in the annular indentation 12. Between the indicator piece 18 and the folded tongues 8 is arranged a coiled spring 23 which urges the indicator piece 18 against the tension of the coiled portion 19 of the resistor wire 17 to project the indicator piece 18 to the position shown in FIG. 4 when the fuse element 16 is ruptured.

Thus, it is necessary to make the spring force of the coiled spring 23 weaker than that of the coiled portion 19 of the resistor wire 17.. The indicator piece 18 needs not to be provided if it is notdesired to indicate the ruptured state of the fuse element. In this case it is not always necessary to make the insulating core 1 hollow and hence to provide the resistor wire 17.

The small cylinder portion 7 of the internal electrode 3 is inserted into the center opening 13 of the external electrode 10 and the tongues 8 constituting the small cylinder portion 7 are radially folded as shown in FIG. 2 and the tongues 8 thus folded are secured to the annular indentation 12 by preferably soldering. Thus, a positive electrical connection between the fuse element 16 of the one hand and the internal electrode 3 and external electrode 10 on the other hand is possible.

In order to provide a current-limiting fuse which will reliably interrupt a low fault current, the fuse element 16 may include substantially at its center part a low melting pointalloy portion 25 incorporated therein and a Teflon sleeve 24 spaced around the low melting point alloy portion 25 as shown in FIG. 10. The low melting point'alloy portion 25 may suitably be formed of at least one of .low melting point alloys selected from the group consisting of Au-Si, Ag-Sn' and Ag-Pb which will form alloys-with the metal of the fuse element 16. The Teflon sleeve 24 may be of about 50 mm in length and located substantially at the intermediate part of the fuse element 16 as shown in FIG. 9. The low melting point alloy portion 25 and the Teflon sleeve 24, however, are not restricted in their location along the fuse element 16.In FIG. 9 the fuse element 16 and the Teflon sleeve 24 are shown as separated fromtheinsulating core 1 for'ease of illustration, but inpractice they are closely wound around the ridges 2 of the insulating corel.

As stated hereinbefore, the current-limiting fuse according to the invention is extremely easy in-as'sembling thefuse element in position as compared to prior art current-limiting fuses. I

In the currentrlimiting fuse according to the invention if the interphase'short circuit, overload or other faultscause the overcurrent to flow'therethrough it becomes melted off and immediately thereafter the resistor wire 17, coiled portion 19 thereof and tension resisting portion 2-1 enclosed in the insulating core 1 are subjected to overvoltage and instantaneously melted off. In this case heat is generated in all of the resistor wire 17 inclusive of the COIIGCI'POI'IIGII 19 and linear tension resisting portion 21 to melt off the resistor wire 17 at several points simultaneously. The heat insulating tube 22 surrounding the tension resisting portion 21 is capable of facilitating the melting ofi of the resistor wire 17 in a positive and safe manner.

The indicator piece 18 thus released is projected out of the external electrode by the action of expansion of the coiled spring 23 thereby indicating the ruptured state of the fuse element 16. I

As seen from the above, the invention provides a totallyenclosed current-limiting fuse whichcan positively indicate the ruptured state of the fuse element The fuse element according to the invention will now be described in idtails. g i i J The fuse element according'to the'invention'consists of a plurality of fuse wires and is not limited to two fuse wires, but'the fuse element consisting-oftwo-"fuse elements will now be described for ease of illustration with referenceto FIGS. 5 to 8. I

which is located near the line III-III of FIG. 5a and rolled by the highest pressure. That is, the center part of the fuse element is rolled such that eachof the two fuse wires is pressed into a thin plate shape. The degree of press rolling subjected to the two fusewires are gradually decreased towards their ends where they are.

merely twisted together without being subjected to any press rolling. Thus, the portions of intersection C where the two fuse wires cross each other asshown in FIG. Se is one half smaller in thickness than the" original nonrolled fuse wires and is is also narrower in width (W) than the'rolled portion P of one fuse wire, with the result that the sectional area and thermal capacity of the portions of intersection C become smaller than those of the rolled portion P, This tendency becomes gradually decreased towards each end of the fuse wires. i The results of experimental tests of the fuse element according to the invention (A), the conventional wire drawn or plate-shaped fuse element (B) and the conventional fuse element with a number of reduced portions arranged discontinuously along its axis (C) under such circuit conditions that applied voltage is 7 KV and prospective interrupting current flows through a phase line in the absence of the current-limiting fuse are shownin FIGS. 8a, 8b and 8c and listed in the following 7 table; J

Conventional Fuse element overvoltage Drawn or plate-shaped Fuse element according to the invention (A) fuse element (B) along its axis (C) l 19.3 xv 39.8 xv 2 8.8 xv

, above table, the conventional unitary fuse element In FIGS. 5a to 5e, there are shown apreferred embodiment of the fuse element according 'tofthe invention in. which use is made of one round fuse wire folded at its center into two fuse wire portions or use may be made of two round fuse wires. These two fuse wires portions or .two fuse'wires aretwisted together into a rope-shaped element which is then subjected to press rollingby an eccentric roller as of example such that the highest pressure is applied to the center part of the fuse wires and the pressure is continuously decreased towards each end thereof until the lowest pressure substantiallyno pressure is applied to each end thereof.

g FIG. 5b shows no rolled state at each end, FIG. 50

shows a medium rolled state and FIG. 5d shows the center part of the twofuse wires in which they are rolled by the highest pressure. FIG. 5e shows the portions of intersection C of that part of the two fuse wires could not refrain. the overvoltage from sudden rising and hence could not be used as the fuse element and 'the conventional fuse element with a number of reduced portions could not refrain the overvoltage from sudden rising, while the use of the fuse wires twisted together and rolledunder thetwisted state as in the fuse element according to the invention makes it possible to refrain-the overvoltage from sudden rising in a positive manner. 1 y i r Another embodiment of the fuse element according to the invention will now be described with reference to FIGS. 6a, 6b, 6c and 6d. In the present embodiment, use is made of one round fuse wire folded at its center into two fuse wire portions 'or use may be made of two round fuse wires. These two fuse wire portions or two fuse wires are twisted together into a rope shaped ele ment which is then subjected to press rolling such that the same pressure is applied to substantially major part of the fuse'wires except each end where there is substantially no rolling pressure is applied. Thus, the degree of pressing of the fuse element as a whole is not continuously changed. The twisting and press rolling operations, however, cause the cross section of the fuse element to discontinuously change. The cross sections of all of the portions of intersection C of the two fuse wires as shown in FIG. 5e are different from those of the rest thereof, thereby refraining the overvoltage from sudden rising in the same manner as in the fuse element A listed in the above table.

A further embodiment of the fuse element according to the invention will then be described with reference to FIGS. 7a, 7b, 7c, 7d, 7e and 7f. In the present embodiment-use is made of one round fuse wire folded at its center into two fuse wire portions or use may be made of two round fuse wires. These two fuse wire portions or two fuse wires are twisted together into a rope shaped element which is then subjected to press rolling such that the center portion near the line XIXI shown-in FIG.- 7a and eachend of the fuse element are applied substantially no rolling pressure, while the center portion near the line IX--IX of halves of the fuse element is rolled by the highest pressure into a thin plate shape and portions near the lines X-X and VIII- -VIII located between this heavily rolled portion lX--IX on the one hand and the center portion XIXI and each end VlI--Vll, on the other hand are rolled by medium-pressure. Thus, each side of the center portion of halves of the fuse element is subjected to continuously varying pressuresand hence rolled into flat portions which are different in cross section each other. The growth of the arcing when the fuse element thus formed is melted is substantially the same as that of the fuse element A listed in the above table.

The fuse element consisting of two fuse wire portions or two fuse wires twisted together may be rolled into ribbon form of uniform section. The fuse element for low current interruption and shown in FIGS. 9 and 10 operates as follows.

If the minimum current for melting the fuse, i.e., the minimum melting current flows through the fuse element 16, the low melting point alloy portion 25 begins to melt to form a slightly melted gap therein and then the arcing current flows therebetween, The arcing energy thus produced causes the low melting point alloy portion 25 to melt. The heat produced by the arcing effect causes the Teflon sleeve 24 spaced surrounding the low melting point alloy portion 25 to generate arc quenching gas'which effects to quench the arc in a'positive manner. The are quenching action of the Teflon is believed to-be due to the 'electronegative character of fluoro gases, which are the main components of decomposition of the Teflon.

As stated above, the Teflon sleeve 24 serves to improve the low current interruption performance of high voltage current-limiting type fuses. I

The Teflon sleeve 24 spaced around a portion of the fuse element 16 of silver or other suitable material such as copper is deteriorated by the temperature rise occurred when current normally flows through the fuse element 16 with the result that there is riskof the arc quenching action of the Teflon sleeve 24 being decreased when the fuse element 1.6 is melted so that interruption becomes impossible. In order to prevent such disadvantage, the low melting point alloy portion 25 is incorporated in the fuse element 16 and the Teflon sleeve 24 is positioned symmetrically with reference to the low melting point alloy portion 25. The presence of the low melting point alloy portion 25 within the Teflon sleeve 24 makes it possible to prevent deterioration of the Teflon sleeve 24 and hence prevent decrease of the arc quenching action of the Teflon sleeve 24 when the fuse element 16 is melted. thereby interrupting reliably a low fault current.

As stated hereinbefore, the current-limiting fuse according to the invention is capable of attaining conspicuously efficient overvoltage refraining effect and of interrupting reliably fault currents with small amount of arc quenching filler, thereby reducing the weight and volume of the fuse to one-half lesser than those of the conventional fuse.

Moreover, a Teflon sleeve and low melting point alloy assembly can overcome the disadvantage of the conventional fuse which could not interrupt reliably a low fault current. As a result of this, the invention has the additional advantage that reliable interruption over the fullrange of fault currents is possible. Thus, the current-limiting fuse according to the invention is applicable to current receiving installations and any other installations in various fields. 1

It will be understood that modifications and variations may be effected without departing the scope of the novel concepts of the present invention.

What is claimed is:

l. A high voltage current-limiting fuse including at least onefuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, an insulating core with said fuse element would spirally with a given pitch, an insulating tube spaced around said insulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each end face thereof, a pair of internal electrodes each provided at one end with a skirt portion for securing said insulating core thereto and provided at another end with a plurality of tongues extending through said center opening of the external electrode and radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, and an arc quenching filler surrounding said insulating core within said insulating tube.

2. A high voltage current limiting fuse as claimed in claim 1, wherein the number of sai d fuse wires is two.

3. A high voltage current-limiting fuse as claimed in claim 1, said insulating core comprising on its outer surface a plurality of ridges spaced from one another and extending in parallel fashion along the length of the core, whereby the core has a star-shaped cross-section.

4. A high voltage current-limiting fuse as claimed in claim 1, wherein said skirt portion of the internal electrodes is provided with a plurality of tongues and slits 5. A high voltagev current-limiting fuse including at least one fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state and including a low melting point alloy portion incorporated therein, a Teflon sleeve spaced around said low melting point alloy portion, an insulating core with said fuse element wound spirally with a given pitch, an insulating tube spaced around said insulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each end face thereof, a pair of internal electrodes each provided at one end with a skirt portion for securing said insulating core thereto and provided at another end with a plurality of tongues extending through said center opening of the external electrode. and radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, and an arc quenching filler surrounding said insulating core within said insulating tube.

6. A high voltagecurrent limiting fuse as claimed in claim 5, wherein said low melting point alloy portion is formed at least one of a low melting point alloy selected from the group consisting of Au-Si, Ag-Sn and Ag-Pb.

" 7. A highvoltage current-limiting fuse as claimed in claim 6, wherein said low melting point alloy consisting of Au-Si alloy. o

8. A high voltage current-limiting fuse including at least one fuse element comprising a plurality of fuse wi jes twisted together, with at least the main portion thereof being press rolled under the twisted state, a hollow insulating core with said fuse element wound spirally withfla given pitch, an insulating tube spaced around said insulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each'end face thereof, a pair of internal electrodeseach provided at one end'with a skirt portion for securing said insulating core'thereto and provided at another encl with a plurality of tongues extendingthrough said center opening of the external electrode and radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, an arc quenching tiller surrounding said insulating core within said insulating tube, an indicator piece located on the center opening in the outer end face of one of the external electrodes, a resistor wire'secured at its one end opposite to said indicator piece to the external electrode and secured at its free end through said hollow insulating core to said indicator piece, and a coiled spring for urging said indicator piece outwards.

sulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each end thereof, a pair of internal electrodes each provided at one end with a skirt portion for securing said insulating core thereto and provided at another end with a' plurality of tongues extending through said center opening of the external electrode and'radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, an arc quenching filler surrounding said hollow insulating core within said insulating tube, an indicatorpiece locatedflon the center opening in the outer end face of one of the exlow melting point alloy portion, a hollow insulating core with said fuse element wound spirally with a given a pitch, an insulating tube spaced around said hollow internal electrodes, a resistor wire secured at its one'end opposite to said indicator piece to the external electrode and secured at its free end through said hollow insulating core to said indicator piece, and a coiled spring for urging said indicator piece outwards.

. 11. A fuse element comprising two fuse wires twisted together and press rolled in the twisted state, having less width at intersections in which the two fuse wires cross each other, each fuse wire being smaller in thickness at said intersections than in the surrounding area.

i 12. A fuse element as claimed in claim 11 in which said two twisted fuse wires are of a uniform configuration along the total length thereof.

13. A fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, the number of fuse wires being two, said two twisted fuse wires comprise slightly press rolled center andend regions.

14. A fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, wherein said plurality of twisted fuse wires comprise a heavily press rolled center region, and diminishing rolled sections towards each end of the fuse wires.

15. A fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, wherein said plurality of twisted fuse wires comprise slightly press rolled center and end regions. 

1. A high voltage current-limiting fuse including at least one fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, an insulating core with said fuse element would spirally with a given pitch, an insulating tube spaced around said insulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each end face thereof, a pair of internal electrodes each provided at one end with a skirt portion for securing said insulating core thereto and provided at another end with a plurality of tongues extending through said center opening of the external electrode and radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, and an arc quenching filler surrounding said insulating core within said insulating tube.
 2. A fuse element as claimed in claim 1, wherein the number of said fuse wires is two.
 3. A high voltage current-limiting fuse as claimed in claim 1, said insulating core comprising on its outer surface a plurality of ridges spaced from one another and extending in parallel fashion along the length of the core, whereby the core has a star-shaped cross-section.
 4. A high voltage current-limiting fuse as claimed in claim 1, wherein said skirt portion of the internal electrodes is provided with a plurality of tongues and slits
 5. A high voltage current-limiting fuse including at least one fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twIsted state and including a low melting point alloy portion incorporated therein, a Teflon sleeve spaced around said low melting point alloy portion, an insulating core with said fuse element wound spirally with a given pitch, an insulating tube spaced around said insulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each end face thereof, a pair of internal electrodes each provided at one end with a skirt portion for securing said insulating core thereto and provided at another end with a plurality of tongues extending through said center opening of the external electrode and radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, and an arc quenching filler surrounding said insulating core within said insulating tube.
 6. A high voltage current-limiting fuse as claimed in claim 5, wherein said low melting point alloy portion is formed at least one of a low melting point alloy selected from the group consisting of Au-Si, Ag-Sn and Ag-Pb.
 7. A high voltage current-limiting fuse as claimed in claim 6, wherein said low melting point alloy consisting of Au-Si alloy.
 8. A high voltage current-limiting fuse including at least one fuse element comprising a plurality of fuse wires twisted together, which at least the main portion thereof being press rolled under the twisted state, a hollow insulating core with said fuse element wound spirally with a given pitch, an insulating tube spaced around said insulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each end face thereof, a pair of internal electrodes each provided at one end with a skirt portion for securing said insulating core thereto and provided at another end with a plurality of tongues extending through said center opening of the external electrode and radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, an arc quenching filler surrounding said insulating core within said insulating tube, an indicator piece located on the center opening in the outer end face of one of the external electrodes, a resistor wire secured at its one end opposite to said indicator piece to the external electrode and secured at its free end through said hollow insulating core to said indicator piece, and a coiled spring for urging said indicator piece outwards.
 9. A high voltage current-limiting fuse as claimed in claim 8, wherein said resistor wire is provided over its intermediate region with a coiled portion and provided at each end thereof with a rectilinear portion.
 10. A high voltage current-limiting fuse including at least one fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state and including a low melting point alloy portion incorporated therein and a Teflon sleeve spaced around said low melting point alloy portion, a hollow insulating core with said fuse element wound spirally with a given pitch, an insulating tube spaced around said hollow insulating core, a pair of external electrodes closing the ends of said insulating tube and having a center opening at each end thereof, a pair of internal electrodes each provided at one end with a skirt portion for securing said insulating core thereto and provided at another end with a plurality of tongues extending through said center opening of the external electrode and radially folded upon the outer end face of the external electrode for electrically connecting each end of the fuse element to the external electrode, an arc quenching filler surrounding said hollow insulating core within said insulating tube, an indicator piece located on the center opening in the outer end face of one of the external electrodes, a resistor wire secured at its one end opposite to said indicator piece to the external electrode and secured at its free end through said hollow insulating core to said indicator piece, and a coiled spring for urging said indicator piece outwards.
 11. A fuse element comprising two fuse wires twisted together and press rolled in the twisted state, having less width at intersections in which the two fuse wires cross each other, each fuse wire being smaller in thickness at said intersections than in the surrounding area.
 12. A fuse element as claimed in claim 11 in which said two twisted fuse wires are of a uniform configuration along the total length thereof.
 13. A fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, the number of fuse wires being two, said two twisted fuse wires comprise slightly press rolled center and end regions.
 14. A fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, wherein said plurality of twisted fuse wires comprise a heavily press rolled center region, and diminishing rolled sections towards each end of the fuse wires.
 15. A fuse element comprising a plurality of fuse wires twisted together, with at least the main portion thereof being press rolled under the twisted state, wherein said plurality of twisted fuse wires comprise slightly press rolled center and end regions. 